{- This file is part of funbot.
 -
 - Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
 -
 - ♡ Copying is an act of love. Please copy, reuse and share.
 -
 - The author(s) have dedicated all copyright and related and neighboring
 - rights to this software to the public domain worldwide. This software is
 - distributed without any warranty.
 -
 - You should have received a copy of the CC0 Public Domain Dedication along
 - with this software. If not, see
 - <http://creativecommons.org/publicdomain/zero/1.0/>.
 -}

module Data.List.Local
    ( groupByFst
    )
where

-- | Takes a list of pairs and groups them by consecutive ranges with equal
-- first element. Returns a list of pairs, where each pair corresponds to one
-- such range.
groupByFst :: Eq a => [(a, b)] -> [(a, [b])]
groupByFst []          = []
groupByFst ((x, y):ps) =
    let (same, rest) = span ((== x) . fst) ps
    in  (x, y : map snd same) : groupByFst rest
